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## 4th grade

### Unit 11: Lesson 2

Angle introduction# Identifying an angle

CCSS.Math:

Sal matches pictures of angles to their degrees. Created by Sal Khan.

## Want to join the conversation?

- An angle smaller than 90 degrees. an obtuse angle is bigger than 90 degrees but smaller than 180 degrees. A right angle is exactly 90 degrees. A straight angle is exactly 180 degrees(11 votes)

- Isn't it hard to tell without a protractor sometimes?(7 votes)
- sometimes but usualy only if you are looking for precice exact numbers that havent bean rounded to the nearest place value. but if their are answer choises that are very different or you are looking for a ruf estemation, than you can usualy eyeball it.(6 votes)

- Is there a angle bigger then 360(6 votes)
- Yes, we can make angles larger than 360 degrees. Just imagine that the two rays making an angle could be rotated as much as you want.

In one rotation, we get to 360 degrees. In two rotations, you can assume the measure to increase by 2 times, which gives us 720 degrees and so on.

Angle measures can go up to infinite degrees.(8 votes)

- How do I cite Khan Academy as a resource in APA style(7 votes)
- URL: Give the full URL of the web page including the protocol (http:// or https://). To cite a Khan academy video in a reference entry in APA style 7th edition include the following elements: Title of the video: Only the first letter of the first word and proper nouns are capitalized.(4 votes)

- if a angle is 91 degrees can it still be counted as a right angle(4 votes)
- No, it would be an obtuse angle. Even if an angle were 90.1 degrees or 89.99 degrees, it wouldn't be a right angle, because a right angle measures exactly 90 degrees.(6 votes)

- I've watched this video three times and it's still not marked as having been watched. The subtitles aren't showing either so I'm having to follow the transcript. I'm on Google Chrome on the iPad, if that makes a difference(7 votes)
- What is the angle between two hands of a clock at4:30(4 votes)
- If the total clock face represents 360°, then each number on the clock represents an angle of 30° and each minute, 6°. So at4:30the minute hand is at 30*6° = 180° and the hour hand is at 4.5*30° = 135°. Thus the angle between them is 180°-135° = 45°(5 votes)

- but,Sal,it does NOT make any sense, if a 60 degrees is more than 30 degrees,it is LESS than 90 degrees,isn't it?(6 votes)
- is any angle less than 90 degrees?(4 votes)
- How do you understand this?

My answer: Draw a protractor. Simple.(4 votes)

## Video transcript

Match these angles
with their measures. There should be one
angle in each category. We have 30 degrees, 60 degrees,
90 degrees, and 180 degrees. So there's a few that are
very easy to spot out. This angle right over here,
it makes a complete line. So this is clearly 180 degrees. So this one's 180 degrees. The other one that
might jump out at you is this one right over here. This is clearly a right
angle, or a 90-degree angle right over here. So this is 90 degrees. And so we have to think
which of these is 30 and which is 60 degrees? Well, just by
comparing it that way, you know that the one
that opens out more is going to be 60 degrees and
the one that opens out less is going to be 30 degrees. And you can see that
this, the opening here, is half the size of the
opening right over here. So it makes sense that
this is 30, this is 60, and it also makes sense
that this angle is 1/3 the measure of this
angle right over here, that this is 90 degrees. And then if you
were to double this, then this part of the angle
would go all the way out, and you would get
to the 180 degrees. So let's check our
answer and make sure we actually
got this one right. Let's do one more, just for fun. Which of these angles has
a measure of 60 degrees? So there's a couple that we
can immediately rule out. This angle here is clearly
more than 90 degrees. It's an obtuse angle. This angle here is
180 degrees, so we're going to have to pick
between these two. And we can assume that
these are all at scale. So if we know that a right angle
would have this line straight up and down, this looks like
it's 2/3 of the way there. So I would go with this
one right over there. Now, you might say, well,
what about this one? Well, this one looks like it's
about 1/3 of a right angle. If we were to do
2/3, then 3/3, it looks like we would
get to a right angle. So this one looks much
closer to 30 degrees. So which of these angles
has a measure of 60? That one right over there. You could immediately rule
out that one and that one, and then these take a little
bit closer inspection.